1. Field of the Invention
The invention relates to an image recording apparatus configured to record images on sheets of recording media, more specifically to an image recording apparatus configured to feed the recording media by a feeding device comprising a drive roller and a driven roller pressing in contact with drive roller.
2. Description of the Related Art
As shown in FIGS. 18A-18C, a known inkjet-type image recording apparatus is provided with a feed roller pair 103 that feeds a recording sheet S (an example of a recording medium) supplied from a sheet supply tray, not shown, to a platen 102. In this image recording apparatus, recording sheet S is fed by feed roller pair 103 intermittently by a predetermined length, while a carriage 101 having a recording head 100 is slid in a direction perpendicular to a direction where recording sheet S is fed in order to eject ink droplets from nozzles of recording head 100 to recording sheet S. Thus, an image is recorded onto the recording sheet S in a predetermined area.
The intermittent feeding is performed by feed roller pair 103 disposed on an upstream side of platen 102 in the feed direction (hereinafter referred to as the “upstream side”) and an ejection roller pair 104 disposed on a downstream side of platen 102 in the feed direction (hereinafter referred to as the “downstream side”), which have their rotation controlled by a control part, not shown.
Feed roller pair 103 includes a drive roller 105 and a driven roller 106. Drive roller 105 is configured to receive a rotational force transmitted from a motor and be driven. Driven roller 106 is urged by a coil spring 107 to press in contact with drive roller 105. As shown in FIG. 18A, when a leading end of recording sheet S supplied from the sheet supply cassette arrives at feed roller pair 103, it is pinched by drive roller 105 and driven roller 106, and feeding of recording sheet S is started by feed roller pair 103. As the feeding of recording sheet S proceeds, the leading end of recording sheet S is pinched by ejection roller pair 104, and recording sheet S is fed by both feed roller pair 103 and ejection roller pair 104 as shown in FIG. 18B. When the feeding of sheet S further proceeds, a trailing end of recording sheet S is separated from feed roller pair 103 as shown in FIG. 18C, and recording sheet S is fed by ejection roller pair 104 only. Ejection roller 104 also includes drive roller 108 and driven roller 109 as with feed roller pair 103. As ejection roller pair 104 is configured to pinch recording sheet S on which an image has been recorded, a low pressing force of ejection roller pair 104 is set to prevent images from deteriorating.
In the image recording apparatus constructed in this manner, when the trailing end of recording sheet S is separated from feed roller pair 103, a part of the pressing force that feed roller pair 103 applies to recording sheet S in a vertical direction will be translated in the feed direction. At this time, a force that is greater than a feeding force generated by the rotation of drive roller 105 acts on the trailing end of recording sheet S, and recording sheet S is slid on ejection roller pair 104 having the low pressing force and is fed with excessive force. As a result, streaks will be generated on recording sheet S, and the image quality will be deteriorated. This problem is most prevalent with a recording sheet such as glossy paper that is relatively thick and has high stiffness.
To solve the above problem, a known image recording apparatus includes a drive roller and a driven roller that is supported slidably and rotatably in the sheet feed direction. When the trailing end of a recording sheet comes off between drive roller and the driven roller, the driven roller recedes toward an upstream side upon a receipt of reaction force from recording sheet. More specifically, in this disclosed image forming apparatus, a rotary shaft of the driven roller slides in long holes, extending in the sheet feed direction, formed on a holder that supports the driven roller.
Nevertheless, in the known image forming apparatus, the reaction force is applied to the driven roller when recording sheet comes off, and the driven roller slides rearward. Thus, when the driven roller slides, a sliding frictional force is generated which is smaller than the reaction force, toward the downstream side with respect to the sheet feed direction. As the sliding frictional force acts in a direction to push recording sheet, recording sheet may be fed more than necessary. This phenomenon is hereinafter referred to as “excessive feeding.” The excessive feeding may lead to a reduction of image quality that cannot be overlooked in high-resolution image forming apparatuses.